This application is based on and incorporates herein by reference Japanese Patent Application No. 2002-250438 filed on Aug. 29, 2002.
1. Field of the Invention
The present invention relates to a throttle valve system of an internal combustion engine capable of preventing freezing of a throttle valve. More specifically, the invention relates to the throttle valve system having a function for preventing the freezing of the throttle valve, which is caused by water coming along an inner peripheral surface of an intake pipe from an upstream side of the throttle valve during a cold period such as a winter season. The present invention also relates to downsizing of a bore portion of a throttle body, in which the throttle valve is accommodated and held rotatably.
2. Description of Related Art
In a cold period such as a winter season, PCV water enters a bore portion 102 of a throttle body from an upstream side of a throttle valve 101 along an inner peripheral surface of an intake pipe and is trapped at a blocked position of the throttle valve 101 as shown in FIG. 13. Then, the PCV water is frozen there. The PCV water is, for example, water flowing from a positive crankcase ventilation system into the intake pipe through an outlet port located upstream of the throttle valve 101. As a result, malfunction of an internal combustion engine may be caused. Therefore, a throttle valve system for overcoming such a problem has been proposed.
For instance, in a throttle valve system disclosed in Japanese Patent Unexamined Publication No. H09-32590 (Pages 3 to 5, FIGS. 1 and 2), a bore portion 202 of a throttle body has double-tube structure, in which an inner bore tube 212 and an outer bore tube 211 are integrally formed of heat-resistant resin, as shown in FIG. 14. The inner bore tube 212 is formed inside the outer bore tube 211 concentrically with the outer bore tube 211. A longitudinal length of the inner bore tube 212 in a direction of intake-air flow is a little shorter than that of the outer bore tube 211. The inner bore tube 212 forms an intake air passage 203. A throttle valve 201 is installed through a shaft at the middle of the longitudinal length of the inner bore tube 212. An annular disk-like partition wall 204 is disposed between the outer bore tube 211 and the inner bore tube 212 through an entire circumference nearly at the middle of the longitudinal length of the inner bore tube 212 in a flat plane perpendicular to the intake-air flow direction. Thus, the partition wall 204 divides an annular space formed between the outer bore tube 211 and the inner bore tube 212 into upstream and downstream trapping concavities (water trapping grooves) 221, 222 for trapping the upstream PCV water flowing into the outer bore tube 211 of the throttle body along the inner peripheral surface of the intake pipe.
As explained above, in the conventional throttle valve system shown in FIG. 14, the central axis of the outer bore tube 211 is arranged concentrically with the central axis of the inner bore tube 212. Furthermore, the annular space between the outer bore tube 211 and the inner bore tube 212 is separated by the annular disk-like partition wall 204 through the entire circumference. Therefore, the trapping concavities 221, 222 are provided with uniform radial width throughout the circumference. Consequently, there arises such a problem that the radial size of the bore portion 202 of the throttle body increases, so the bore portion 202 is upsized.
In addition, a flowing pattern or flowing quantity of the water flowing from the upstream side or the downstream side of the throttle valve varies in accordance with a layout of an intake system of a vehicle, a mounting position of an idling speed control valve (ISC valve), and a mounting position of the throttle body to the vehicle. The ISC valve is used for controlling the idling rotation speed of the engine by regulating the quantity of air flowing through a bypass of the throttle valve. Therefore, trapping concavities having required size should be preferably provided in optimum positions in accordance with the flowing condition of the water flowing into the throttle body.
It is therefore an object of the present invention to provide a throttle valve system of an internal combustion engine capable of providing a space, an annular space or a trapping concavity having a required size at an optimum position in accordance with flowing condition of water flowing into a throttle body. It is therefore another object of the present invention to provide a throttle valve system of an internal combustion engine capable of preventing freezing of the throttle valve without introducing engine cooling water, while downsizing the throttle body.
According to an aspect of the present invention, a throttle body has double-tube structure, in which an outer bore tube radially surrounds an outer peripheral surface of an inner bore tube. The inner bore tube accommodates a throttle valve so. that the throttle valve can open or close. The double-tube structure is formed so that a radial distance between the inner bore tube and the outer bore tube at a certain position differs from the radial distance between the inner bore tube and the outer bore-tube at another position. A space formed, between the outer periphery of the inner bore tube and the inner periphery of the outer bore tube is located in a required size at an optimum position in accordance with flowing condition of water entering the throttle body. Thus, the water can be surely trapped in the space even if a flowing pattern or flowing quantity of the water flowing in from an upstream side or a downstream side of the throttle valve changes due to a change in a layout of an intake system of a vehicle, a mounting position of an ISC valve, or a mounting position of the throttle body to the vehicle. As a result, freezing of the throttle valve can be prevented without introducing engine cooling water.
According to another aspect of the present invention, the throttle body is formed in the double-tube structure, in which the inner bore tube is formed in the outer bore tube so that the central axis of the inner bore tube is deviated from the central axis of the outer bore tube. Thus, the radial size of the throttle body is reduced, so the throttle body is downsized.